Recent studies, in humans and other animal species, indicate that marrow stromal cells (MSC) are multipotent and have potential use in treatment of disease. The development of a non-rodent, non-inbred large animal model system is critical to fully understand the biological mechanisms involved and to explore potential use of such cells in disease therapies for humans. Cats are uniquely suited for basic research of biologic and disease processes, particularly in developmental biology, normal physiology, and animal modeling of human inherited, infectious and neoplastic diseases. The goal of this project is to develop feline marrow stromal stem cell model systems that can then be used to study safety and efficacy of stem cell transplantation therapy. Protocols will be developed for optimal isolation and expansion of MSC from bone marrow of normal cats. Methods will be optimized to separate these multipotential progenitor cells from other cells in bone marrow. Media components, seeding densities and growth factor effects on short term and long term passage in vitro will be evaluated. Optimal age of donor cats also will be investigated. A comprehensive characterization of feline MSC in vitro based on markers of gene expression and on peptide affinity technology will be accomplished. The potential of feline MSC to differentiate to various cell phenotypes based on media manipulation will be explored. The distribution and fate of feline MSC following in vivo transplantation will be studied. Feline MSC will be harvested, labeled with a reporter gene, injected by several routes back into the same individual, and analyzed at various time points to track these cells in different organs. Similar trafficking studies will be done with cells phenotypically differentiated in vitro to determine their fates.